Induction-motor system.



Patented Aug. 14, 1917.

2 SHEETS-SHEET I.

H F. STRATTOM INDUCTION MOTOR SYSTEME APPLICATION mso APILZB 191a.

INVENTOR *v vwam BY it ATTORNEY Mugs/5M4 H. F. STRATTON.

INDUCTION MOTOR SYSTEM.

armcmou FILED "12.29. 1913.

Patented Aug. 14, 1917.

INVENTOR WITNESSES UNITED TArEs PATENT OFFICE- naniir r. s'ma'rron,OF'CLEVELAND, onro, vnssicnoa, BY MrisNnAssxeNMEN'rs, r0

,THE ELECTRIC CONTROLLER & MANUFACTURING COMPANY, A CORPORATION OF OHIO.

Specification of lietters'latent.

rmiuc'rroixi moron SYSTEM.

Pat'eritedAug. 14, 1917.

:Original application filed J'u1y'27, 1911, SerfaU-No. 1540;885. Dividedand this application filed April 29,

' 1913. Serial Nix-7643M. a i

To all whom it may concern: r. I; t

Be it known that I, HARRY F. Sma'ri oN, a citizen of the United States,vresiding at Cleveland, in the county of Cuyaho'ga: and State of Ohio,have invented new and ruseful Improvements in Induction-Motor :Systems,of which the following is a specifies, tion. 1

'My invention broadly relates to electric controlling devices whichemploys one -.or more magnetically-operated switches to control the flowof current; more particularly, it relatesto a controller foralternating' current motors of the induction typefby which controllersuch a-motor may be lstarted by automatically cutting resistance-outofthe secondary circuit of the motor. I :make use of magnetically-operatedswitches,'-each; of whose operating windings is connected in selies withthe secondary circuit and shortcircuited on closureof the switchcontacts. I provide for each switch a holding, or maintainingmagnetwhich is excited i from .the primary circuit and does not necessarilyaid in operating the switch, but is. merely used to hold the switchclosed after ithas operated. The operating winding being in circuit onlyWhile the switch isbeingactuated, its magnetic circuit or frame does notneed to be laminated. The holding magnet needs to be only strong enoughIto hold'the switch closed, and therefore, by-aproper construction ofparts: the force it must exert can be made smaller than would berequired for-o erating the switch throughits whole move ment. I preferalso to so construct the switch that the pull ofthe holding magnet ismultiplied through a lever mechanism thereby reducing the -size of theholding magnet and the amount of current required for exciting it. Sincethe holding magnet is energized during the whole'time that thecontroller is in service, its magnetic circuit should be laminated, or,at least, that part which is embraced by the winding.

I consider a controller employing a switc constructed in such a manneras just described, which has an operating winding adapted. to beconnected in circuit only a short period, its magnetic circuit being notlaminated, =and a holding magnet ofsmall size with more or less of itsmagnetic circuit laminated more desirable than the usual type ofalternating current switch with a single winding-which must belarge-enough to operate the switch and-*hold --it closed. Hlhel'atter'type of switch 'is usually constructed with toggle joints"andspring contact devices which are obj e'ctionable onaccountdfvthe'dargemember of small parts requiredfor each-switch.Inord'erYtomor'e fully describe my inventionaI will refer totheaccompanying drawing s 'i'nl'which- Figure 1 is a; vertical section of aswitch, constructed -in accordance with my inventiony partst beingin-"s'ide elevation; Fig. 2, a front view ofthewswitolr;Figs. 3 and 4,sectional viewsshowing t'wo methods'of con- "structimg the holding, jOIimaintaining, magnets;"F=ig. 5, a wiiingxdiagram of the connections:Eora-n-induotion motor starter; and Figs; =6 1 and 7, dia-g'rams 1showing alternate methods'ofi'conn'ecting the holding windings of theswitches. I v Referring to :Figs. 1 and 2, S represents a frame ofmagneticmaterial bolted to the insulating support 8- and containing thewinding S which hasanaxial opening. In the upper part; of this openingis the "steel pl-u-g S provided with the flange S resting on theframe-S. @Theecoil-holding sleeve S surrounds the upper *end of' theplug and is screwed intothe top of the frame S. The steel'plu'nger-S isseated in the axial opening-inthecoilbelow the plug S and is connectedto the lower end of the non-magnetic rod S which extends :upthrough theplug S. and carries the contact-plate holder S at its upper end. S 9 isthe-contact-plate on thetop of the holder's". and is arranged to connecttogether the three brushes S, S 8, supported by suitable-fixed'contac'tholders, of-which one only, marked S, isshown. S is an adjustablesleeveof magnetic material which surrounds the reduced lower end of-theplunger S and is screwed into the lower portionof the frame S. The nut5" working on the sleeve and bearing against thebottom of the frameserves as a lock-nut for the sleeve.

The switch just-referred to is fully described in Cainfieldlsapplications, Serial Numbers 583.000 and 604,331, and in East- .woodsPatent No; 1,040,292 granted October 8, 1912. This switch is peculiar inthat, when its'winding S is'energized above a predetermined value, theplunger S is ing, or.g.,maintaining,--magnet S referred to. It has alaminated core or frame andunay have as in Fig. 3, a single winding S",or a-number ofiwindings S and S on separate.-cores,ia's shown on Fig.-4.- 1

S is the armature of the-magnets. and is mountedon :thepivot S so thatits lower end :may swing'toward and from the magnet its free end incontact 'with' the lower end of the reduced extensio'n of the plungerS". The material of the' armature is distributed so that, if free toact, its lower-end will swing toward the magnet S R If-both coils aredenergized, the weight of the plunger S and the parts supported therebycauses the armature S tomove into the-postion shown in the drawing. Whenin this position,'=the magnet S cannot pull the armature S acrossthe:wide. air-gap between itself and the adjacent :poles of the magnetandtherebyoperate the switch; but when the'switch is operated-by thewinding S,- the armature S swings by ravity toward the-magnet S", thefinger S following the lower end of the plunger S When the armatureS'*'has moved so as to reducethe said air-gap sufiiciently,'it willbe-acted upon by-the ma et S with sulficientforce to hold the switchcontact plate S against the said contact brushes; and thewinding S may,therefore, be deenergized as soon as the contact plate S has engaged thebrushes.

In order that the force exerted by the magnet S on the armature S may bemuch less than that required between the contact plate (3 and thecontact brushes, I have arranged the armature S so that the magnet Swill act upon it at a greater distance from the fulcrum S than the forceexerted by the contact brushes. By this arrangement I can use acomparatively small holding magnet which is cheap to construct.

The power required to hold the switch closed is also reduced to aminimum.

Iii-Fig.- 3, I have shown the magnet S with a single coil S to beconnected across onepair of the primary mains; and in Fig. 4 I haveshown the magnet S with two coils S and S which may be connected acrosstwo different pairs of the primary mains, thereby forming a polyphasemagnet exerting at-all times an attraction on the armature S and therebyreducing the chatter or noise to a minimum.-

Referring now to the wiring diagram of the system of control shown inFig, 5,- the primary wires 1, 2, 3, of the induction motor V M areenergized by closing the switch K.

The secondary-wires 5, 6, 7 have resistances 8 to 16 arranged tobe'short-circuited in rou ,s .by the closure of the switches S, S";constructed as shown in Figs. 1 and 2. "When the main switch Kis.closed, current flows in the primary wiresl, 2, and 3 and throughthe-holding windings S, which are connected in series across the Wires 2and 3. Current in the secondary wires 5, 6, and 7 is controlled bythe-resistances '8 to 16. The-first rush ofcurrent in the winding Softtheswitch S, which is connected across the resistances 9 and 10, willbe suflicient to lock the switch S open. The switch S remains-lockedopen until the current-in its winding decreases to a pointat which theswitch is adjusted to operate, at which time it'will closeits'contactsand short-circuit the resistances-8,- 9, and 10 'and its operatingwinding- S The winding S below the switch holds the latter closed.

' The closure ofthe switch S 'also causes the winding S -ofthe' switch Sto be energized." The increased amount-of current in the secondarycircuit due to the cutt-ingout of the resistances 8, 9, and 10 causesthe switch S -.to be lcckedopen until the current in its winding-dropsto a predetermined value, at which time the switch S closes,

short-circuiting the resistance's 11, 12, and 13 and the winding S ofthe switch S which remains closed due to its holding coil S The closureofthe switch S causes the winding S of the switch S to receive current.This switch is then locked open by the increase of current in thesecondary circuit. When the current again decreases to a predeterminedvalue the switch S closes, shortcircuiting the remaining group ofresistances 14, 15, and 16and its own operating wind ing S, the switchbein then held closed by its holding winding- The secondary windings ofthe motor are now entirely short-circuited, and the motor operates atits normal speed. I

When it is desired to stop the motor the switch K is opened, which cutsoil' the motor current. The holding windings S are also deenergized bythe opening of the switch K, and the switches S, S", S drop open.

'Since the resistance controlling switches cannot open until the mainswitch K is opened, the contacts of the switches S, S", S do not carrycurrent at the time the switches open, making it unnecessary to provideblow-out magnets or other devices for extiguishing arcs.

I have shown the actuating windings of the three accelerating switchesconnected in different phases, but it is obvious that they can all beconnected in the same phase without altering the principlesof the systemdescribed. a

I have shown the holding magnets in Fig. 5 as bein single-phase m.- \etsconnected in series, that they may be connected in parallel.

In Figs. 6 and 7 I have shown the holding windings on each switcharranged to be excited on more than one pair of leads, each holdingmagnethaving two windings S. These windings may be connected in parallel, as shown in Fig. 6, or in series, as shown in Fig. 7. Since thecurrent in one winding 9 of a holding magnet is out oiphasc with thecurrent in the other winding S there is always a resultant magnetizationwhich prevents the chattering of the switch'parts.

In the type of motor shown where resistances are used in the secondcircuit of the motor to vary its speed, the windings receiving ci'icrgyfrom the secondary circuit of the motor are subjected to a current whosefrequency gradually diminishes. When the frequency becomes very low thetime between maximum magnetization in one direction and the maximummagnetization in the other direction is so great that, in the case of aswitch, the switch would open and close its contacts in step with thefrequency. By placing the maintaining windings in the primary circuitwhere the windings are subjected to a current of substantially constantfrequency, the switch would remain closed.

Although I have shown my invention applied to a three-phase system, itwill be understood that it can be readily adapted for use in asingle-phase or any polyphase system.

This application is a division of my application, Serial Number 640,885,filed July 27, 1911, which has matured into Patent No. 1,134,422. April6, 1915.

I claim 1. In a system of control, an induction motor, resistance in thesecondary circuit of the notor, magnctically-operated switches forcontrolling the resistance, each switch having an actuating windingenergized by current in the secondary circuit which de- .lays theclosure of the switch and also closes it, each switch in closingshort-circuiting its winding and a portion of the resist ance, and aseparate magnet for holding each swil ch closed energized by current inthe primary circuit.

2. In a system of control, an induction motor, resistance in thesecondary circuit of the motor, a plurality of magneticallyoperatedacceleration switches for controlling the resistance, anormally-decnermzed actuating winding for each acceleration switchenergized by current in the secondary circuit, and delaying the closureof its switch at it will be readily understood the motor, a plurality ofelectroma and closing the same, and a separate magrift being a switchfor each group, an operating winding for the first switch of the seriesconnected in series with the resistances of the first group, and anoperating winding for the second switch of the series, the winding ofthe first switch delaying the closure of its switch and closing. thesame to cut out the first group of resistances from the motor circuit.to dei nergize the winding of the first switch, and to connect theoperating winding of the second switch in series with the resistances ofthe second group together with means for holding the switches closed.

4. In a system of control, an induction motor, resistance in thesecondary circuit of etic acceleration switches for controlling t eresistance, a normally decnergized winding for each acceleration switchenergized by current in the secondary circuit and delaying the closureof its switch, and a separate magnet for holding each switch closed,energized by current in the primary circuit, each switch in closingshort-circuiting its own winding and energizing the winding of the nextswitch to close.

5. The combination of an alternating current motor, a plurality ofgroups of resistances therefor. a series of acceleration switches forcutting out the resistances, there being a switch for each group, anenergizing winding for the first switch of the series connected inserieswith the resistances of the first group. and an energizing windingfor the second switch of the series, the winding of the first switchdelaying the closure of its switch. and the first switch on closingcutting out the first group of resistances from. the motor circuit,deenergizing the winding of the first switch and connecting theenergizing winding of the second switch in series with the resistancesof the second group, together with means for holding the switchesclosed.

Signed at'Cleveland. Ohio, this 25th day of April, A. D. 1913.

HARRY F. STRATTON.

Witnesses:

J. H. HALL, H. M. DIEMER.

It, is hereby vertified that in Letters Patent. No. 1,237,221), grantedAugust 14.

1917, upon the application of Han-r3 l". Stratum, ul' Lieveluml, Ohio,for an improvement in huiunion-Mum! Systems," orr0r appear in theprinted specifirntjon requiring; currertinn as follows: Page 2. line 45,I'm' the reference-letter the said Letters Patent should be read with1m.-wmcuom therein that the same may conforrn t0 the record of the easein the Patent Ofl'ice.

Signed and sealed this 2:! day of October, A. D., 1917 [SEAL] F. W. H.CLAY,

.1ctvl'ng Commissioner of Patents. Cl. 172289

